Findings

All sites use width=device-width, with in most cases an additional initial-scale=1. This is good practice.

However:

8 sites turn off pinch-zooming by setting maximum-scale to 1, or using user-scalable=no. While there are some corner use cases for this, it does not make sense to do this on text-heavy sites as it impairs accessibility.

3 sites use semi-colons as delimiters between viewport values. While this works in newer mobile browsers, it’s not officially supported, and breaks in older mobile browser versions.

1 site has 2 viewport meta tags (with different values) in the source…

1 site sets an explicit value for target-densitydpi. While there are some corner use cases for this, it’s better to leave this up to the browser to decide. In this case, the site’s fonts look strangely big on high-DPI screens.